title: NMR-based structure of anticancer drug mitoxantrone stacked with terminal base pair of DNA hexamer sequence d-(ATCGAT)2.
abstract: Mitoxantrone is a promising antitumor drug having considerably reduced cardiotoxicity as compared to anthracyclines. Its binding to deoxyhexanucleotides sequence d-(ATCGAT)2 has been studied by proton and phosphorous-31 nuclear magnetic resonance spectroscopy. The stoichiometry reveals that 1:1 and 2:1 mitoxantrone-d(ATCGAT)2 complexes are formed in solution. Significant upfield shifts in 6H/7H, 2H/3H, 11NH, and 12NH protons (∼.5 ppm) of mitoxantrone and T6NH imino protons (∼.3 ppm) are observed. The phosphorous resonances do not shift significantly indicating that the base pairs do not open at any nucleotide step along the sequence of hexamer. Several inter-molecular Nuclear Overhauser Enhancement connectivities between mitoxantrone and hexanucleotide protons indicate that mitoxantrone chromophore stacks with terminal A1-T6 base pair and side chains involving 12CH2, 12NH, and 14OH protons are in close proximity of A1, T2, A5, and T6 bases. Absorption and emission spectra show red shift in wavelength maxima, which is characteristic of stacking interaction. At higher mitoxantrone to nucleic acid ratios, electrostatic interactions are dominant. The 2:1 drug/DNA stoichiometric structure obtained by restrained Molecular Dynamics simulations shows considerable distortions in backbone torsional angles and helicoidal parameters although structural fluctuations in 25 ps analysis of trajectory are found to be negligible. Mitoxantrone binds as a monomer at either or both ends of hexamer externally with side chains interacting specifically with DNA. The findings are relevant to the understanding of pharmacological action of drug.
authors.affiliation: a Department of Chemistry , National Institute of Technology Hamirpur , Hamirpur , 177 001 , India .
authors.forename: Shilpa
authors.initials: S
authors.lastname: Dogra
authors.forename: Pamita
authors.initials: P
authors.lastname: Awasthi
authors.forename: Sweta
authors.initials: S
authors.lastname: Tripathi
authors.forename: T P
authors.initials: TP
authors.lastname: Pradeep
authors.forename: Maya S
authors.initials: MS
authors.lastname: Nair
authors.forename: Ritu
authors.initials: R
authors.lastname: Barthwal
mesh_terms: D000970:Antineoplastic Agents / Q000737:chemistry*; D001483:Base Sequence; D004247:DNA / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008942:Mitoxantrone / Q000737:chemistry*; D056004:Molecular Dynamics Simulation
chemical_list: D000970:Antineoplastic Agents; D004247:DNA; D008942:Mitoxantrone
keywords: NMR studies; Restrained Molecular Dynamics simulations; drug–DNA interactions; external stacking; mitoxantrone-d(ATCGAT)2 complex